Dosimetric dependence on the collimator angle in prostate volumetric modulated arc therapy

Muhammad Isa, Jalil ur Rehman, Muhammad Afzal, James Chow


Purpose: The purpose of this study is to investigate the dose-volume variations of planning target volume (PTV) and organs-at-risk (OARs) in prostate volumetric modulated arc therapy (VMAT) when varying collimator angle. The collimator angle has the largest impact and is worth considering, so, its awareness is essential for a planner to produce an optimal prostate VMAT plan in a reasonable time frame.

Methods: Single-arc VMAT plans at different collimator angles (0o, 15o, 30o, 45o, 60o, 75o and 90o) were created systematically using a Harold heterogeneous pelvis phantom. The conformity index (CI), homogeneity index (HI), gradient index (GI), machine monitor units (MUs), dose-volume histogram and mean and maximum dose of the PTV were calculated and analyzed. On the other hand, the dose-volume histogram and mean and maximum doses of the OARs such as the bladder, rectum and femoral heads for different collimator angles were determined from the plans.

Results: There was no significant difference, based on the planned dose-volume evaluation criteria, found in the VMAT optimizations for all studied collimator angles. A higher CI (0.53) and lower HI (0.064) were found in the 45o collimator angle. In addition, the 15o collimator angle provided a lower value of HI similar to the 45o collimator angle. Collimator angles of 75o and 90o were found to be good for rectum sparing, and collimator angles of 75o and 30o were found to be good for sparing of right and left femur, respectively. The PTV dose coverage for each plan was comparatively independent of the collimator angle.

Conclusion: Our study indicates that the dosimetric results provide support and guidance to allow the clinical radiation physicists to make careful decisions in implementing suitable collimator angles to improve the PTV coverage and OARs sparing in prostate VMAT.


VMAT; Dose-Volume Histogram; Collimator Angle; Organs-At-Risk

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Yu CX. Intensity-modulated arc therapy with dynamic multileaf collimation: an alternative to tomotherapy. Phys Med Biol 1995; 40:1435-49.

Webb S, McQuaid D. Some considerations concerning volume-modulated arc therapy: a stepping stone towards a general therapy. Phys Med Biol 2009; 54:4345-60.

Otto K. Volumetric modulated arc therapy: IMRT in a single gantry arc. Med Phys 2008; 35:310-7.

Bzdusek K, Friberger H, Eriksson K, et al. Development and evaluation of an efficient approach to volumetric arc therapy planning. Med Phys 2009; 36:2328-39.

Palma D, Vollans E, James K, et al. Volumetric modulated arc therapy for delivery of prostate radiotherapy: comparison with intensity-modulated radiotherapy and three-dimensional conformal radiotherapy. Int J Radiat Oncol Biol Phys 2008; 72:996-1001.

Hardcastle N, Tome WA, Foo K, et al. Comparison of prostate IMRT and VMAT biologically optimized treatment plans. Med Dosim 2011; 36:292-8.

Guckenberger M, Richter A, Krieger T, et al. Is a single arc sufficient in volumetric-modulated arc therapy (VMAT) for complex-shaped target volumes? Radiother Oncol 2009; 93:259-65.

Alvarez-Moret J, Pohl F, Koelbl O, Dobler B. Evaluation of volumetric modulated arc therapy (VMAT) with Oncentra Master Plan® for the treatment of head and neck cancer. Radiat Oncol 2010; 5:110.

Iori M, Cattaneo G, Cagni E, et al. Dose-volume and biological-model based comparison between helical tomotherapy and (inverse-planned) IMAT for prostate tumors. Radiother Oncol 2008; 88:34-45.

Zhang P, Happersett L, Hunt M, et al. Volumetric modulated arc therapy: planning and evaluation for prostate cancer cases. Int J Radiat Oncol Biol Phys 2010; 76:1456-62.

Wolff D, Stieler F, Welzel G, et al. Volumetric modulated arc therapy (VMAT) vs. serial tomotherapy, step-and-shoot IMRT and 3D-conformal RT for treatment of prostate cancer. Radiother Oncol 2009; 93:226-33.

Men C, Romeijn HE, Jia X, Jiang SB. Ultrafast treatment plan optimization for volumetric modulated arc therapy (VMAT). Med Phys 2010; 37:5787-91.

Rao M, Yang W, Chen F, et al. Comparison of Elekta VMAT with helical tomotherapy and fixed field IMRT: plan quality, delivery efficiency and accuracy. Med Phys 2010; 37:1350-9.

Cao D, Afghan MK, Ye J, et al. A generalized inverse planning tool for volumetric-modulated arc therapy. Phys Med Biol 2009; 54: 6725-38.

Shepard DM, Cao D, Afghan MK, Earl MA. An arc-sequencing algorithm for intensity modulated arc therapy. Med Phys 2007; 34:464-70.

Bedford JL, LeeYK, Wai P, et al. Evaluation of the Delta4 phantom for IMRT and VMAT verification. Phys Med Biol 2009; 54:N167-76.

Letourneau D, Publicover J, Kozelka J, et al. Novel dosimetric phantom for quality assurance of volumetric modulated arc therapy. Med Phys 2009; 36:1813-21.

Korreman S, Medin J, Kjaer-Kristoffersen F. Dosimetric verification of Rapid Arc treatment delivery. Acta Oncol 2009; 48:185-91.

Chow JC, Jiang R. Dosimetry estimation on variations of patient size in prostate volumetric-modulated arc therapy. Med Dosim 2013; 38: 42-7.

Haga A, Nakagawa K, Shiraishi K, et al. Quality assurance of volumetric modulated arc therapy using Elekta Synergy. Acta Oncol 2009; 48:1193-7.

Wolff D, Stieler F, Hermann B, et al. Clinical Implementation of Volumetric Intensity-Modulated Arc Therapy (VMAT) with ERGO++. Strahlenther Onkol 2010; 186:280-8.

Stieler F, Wolff D, Lohr F, et al. A fast radiotherapy paradigm for anal cancer with volumetric modulated arc therapy (VMAT). Radiat Oncol 2009; 4:48.

Dobler B, Weidner K, Koelbl O. Application of volumetric modulated arc therapy (VMAT) in a dual-vendor environment. Radiat Oncol 2010; 5:95.

Kjaer-Kristofferesen F, Ohlhues L, Medin J, Korreman S.RapidArc volumetric modulated therapy planning for prostate cancer patients. Acta Oncol 2009; 48:227-32.

Yoo S, Wu QJ, Lee WR, et al. Radiotherapy treatment plans with RapidArc for prostate cancer involving seminal vesicles and lymph nodes. Int J Radiat Oncol Biol Phys 2010; 76:935-42.

Shaffer R, Morris WJ, Moiseenko V, et al. Volumetric modulated arc therapy and conventional intensity-modulated radiotherapy for simultaneous maximal intraprostatic boost: A planning comparison study. Clin Oncol R Coll Radiol 2009; 21: 401-7.

Boyer A, Biggs P, Galvin J, et al. Basic applications of Multileaf Collimators: report of the AAPM radiation therapy committee Task Group 50. Med Phys 2001.

Jeraj M, Robar V. Multileaf collimator in radiotherapy. Radiol Oncol 2004; 38:235-40.

Bortfeld T. The number of beams in IMRT-theoretical investigations and implications for single-arc IMRT. Phys Med Biol 2010; 55:83-97.

Bortfeld T, Webb S. Single-Arc IMRT. Phys Med Biol 2009; 54:N9-20.

Treutwein M, Hipp M, Koelbl O, et al. Searching standard parameters for volumetric modulated arc therapy (VMAT) of prostate cancer. Radiat Oncol 2012; 7:108.

Feygelman V, Zhang G, Stevens C. Initial dosimetric evaluation of Smart Arc a novel VMAT treatment planning module implemented in a multi-vendor delivery chain. J Appl Clin Med Phys 2010; 11:3169.

Chiarot CB, Siewerdsen JH, Haycocks T, et al. An innovative phantom for quantitative and qualitative investigation of advanced x-ray imaging technologies. Phys Med Biol 2005; 50:N287-97.

Forde E, Kneebone A, Bromley R, et al. Volumetric-modulated arc therapy inpostprostatectomy radiotherapy patients: A planning comparison study. Medical Dosim 2013; 38:262-7.

Paddick I, Lippitz B. A simple dose gradient measurement tool to complement the conformity index. J Neurosurg 2006; 105:194-201.

Otto K. Letter to the Editor on ‘Single-Arc IMRT?’ Phys Med Biol 2009; 54:L37-41.

Fogliata A, Nicolini G, Alber M, et al. IMRT for breast. A planning study. Radiother Oncol 2005; 76:300-10.

Verbakel WF, Senan S, Lagerwaard F, et al. Comments on ‘Single-Arc IMRT? Phys Med Biol 2009; 54: L3.

Rana S, Cheng C. Feasibility of the partial-single arc technique in RapidArc planning for prostate cancer treatment. Chin J Cancer 2013; 32:546-52.

Sze HC, Lee MC, Hung WM, et al. RapidArc radiotherapy planning for prostate cancer: single-arc and double-arc techniques vs.intensity-modulated radiotherapy. Med Dosim 2012; 37:87-91.


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